Rapid reversible changes in dendritic spine structure in vivo gated by the degree of ischemia.

Current therapeutic windows for effective application of thrombolytic agents are within 3-6 h of stroke. Although treatment can improve outcome, it is unclear what happens to synaptic fine structure during this critical period in vivo. The relationship between microcirculation and dendritic spine structure was determined in mouse somatosensory neurons during stroke. Spines were, on average, 13 mum from a capillary and were supplied by approximately 100 red blood cells per second. Moderate ischemia (approximately 50% supply) did not significantly affect spines within 5 h; however, severe ischemia (<10% supply) caused a rapid loss of spine and dendrite structure within as little as 10 min. Surprisingly, if reperfusion occurred within 20-60 min, dendrite and spine structure was mostly restored. These data suggest that the basic dendritic wiring diagram remains mostly intact during moderate ischemia and that affected synapses could potentially contribute to functional recovery. With severe ischemia, markedly deformed dendritic structure can partially recover if reperfusion occurs early.